Food warming apparatus and method

ABSTRACT

A method of preserving cooked food. Food is cooked in a cooking appliance to provide pre-cooked food and placed in a holding compartment of a food warming apparatus for a duration of holding time. The pre-cooked food is heated in the holding compartment for at least a portion of the duration of holding time by delivering in a pre-programmed manner an amount of radiant heat to the pre-cooked food from a radiant heat source positioned above the pre-cooked food. The amount of radiant heat delivered to the pre-cooked food is varied to maintain the food at a selected holding temperature by delivering radiant heat to the pre-cooked food at a first level during a first phase of the duration of holding time and delivering radiant heat to the pre-cooked food at a second level during a second phase of the duration of holding time.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of pending U.S. application Ser. No.10/680,626, filed Oct. 7, 2003, which is a continuation-in-part ofpending U.S. application Ser. No. 10/611,295, filed Jul. 1, 2003, whichclaims the benefit of U.S. Provisional Application No. 60/394,841, filedJul. 10, 2002, titled HOLDING OR COOKING OVEN.

BACKGROUND OF THE INVENTION

This invention relates generally to food service equipment and moreparticularly to equipment for maintaining foods at temperatures suitablefor serving food.

In one embodiment, this invention is especially (but not exclusively)directed to food service equipment that uses infrared (IR) heaters tomaintain pre-cooked food at proper temperatures before serving. Thistype of equipment is referred to using such terms as holding oven,holding unit, and food warmer, and these terms are used interchangeablyhereinafter. Such equipment is often used in, for example, the fast foodservice industry to heat food. However, such equipment has certaindisadvantages. For example, short holding times (e.g., twenty minutes orless) and rapid product quality degradation often limit theeffectiveness of this technology for holding applications. Additionally,different food products require different amounts of IR energy to beheld in optimum condition. The quality of the food being held isaffected in large part by the temperature and the air flow in theholding oven. As the food loses moisture due to evaporation, flavor islost. This affects the texture and taste of the product. For example,chicken meat fibers will dry out and become tough, while the breadingwill become dry and greasy. French fries will develop a dry, rubberytexture as moisture is lost and the outer skin loses its crispness.

Conventional IR holding devices are not adjustable to control the amountof IR energy delivered to the food being heated. Rather, the heat sourceis on full power all of the time, and the food is placed relatively farfrom the heat source to prevent overheating. As a result, the typicalprior holding device requires a large amount of vertical space. This canpresent a problem in a situation where space is at a premium, as in afast-food restaurant.

U.S. Pat. Nos. 6,175,099, 6,262,394 and 6,541,739, assigned to DukeManufacturing Co. of St. Louis, Mo. and incorporated herein byreference, are directed to a holding or cooking oven which is animprovement over prior designs and which has proven to be successfulwith various fried products. However, there is still a need for atechnology that extends the holding time and quality of food products,especially fried products such as hash browns, French fries, rotisseriechicken, deep-fried chicken and shrimp.

SUMMARY OF THE INVENTION

Among the several objects of this invention will be noted the provisionof food service equipment, e.g., a food warmer, which is adapted forholding pre-cooked food longer without degradation of the quality of theproduct, including products having a crust which tends to become soggyor rubbery, such as fried potato products, fried chicken, and rotisseriechicken; the provision of such equipment which is more compact thanconventional food warming equipment, thus requiring less space; theprovision of such an oven which allows evaporative losses to be moreclosely controlled to enhance food quality; and a method of maintainingpreviously cooked food in an environment where the quality of the foodis maintained at a high level for a longer period of time.

In general, one aspect of the present invention is directed to a methodof preserving cooked food. The method comprises the steps of cookingfood in a cooking appliance to provide pre-cooked food, placing thepre-cooked food in a holding compartment of a food warming apparatus fora duration of holding time, and heating the pre-cooked food in theholding compartment for at least a portion of the duration of holdingtime by delivering in a pre-programmed manner an amount of radiant heatto the pre-cooked food from a radiant heat source positioned above thepre-cooked food. The heating step comprises varying the amount ofradiant heat delivered to the pre-cooked food to maintain the food at aselected holding temperature by delivering radiant heat to thepre-cooked food at a first level during a first phase of the duration ofholding time and delivering radiant heat to the pre-cooked food at asecond level during a second phase of the duration of holding time.

In yet another aspect, the invention is directed to a method ofcontrolling a food holding oven. The oven comprises a cabinet, aplurality of separate, thermally isolated holding compartments in thecabinet, a plurality of trays for containing pre-cooked food having beenpreviously cooked in a cooking appliance, each compartment being adaptedfor removably receiving one tray per compartment, and heat sources aboverespective trays adapted for activation to emit radiant heat to the foodin the trays to warm the food. The method of controlling the ovencomprises setting a selected holding temperature for each compartment,setting a duration of holding time for each compartment, the duration ofholding time comprising a duration of heated holding time, and varyingthe amount of radiant heat delivered to the pre-cooked food during arespective duration of heated holding time to maintain the food in arespective compartment at the selected holding temperature.

Other objects and features will be in part apparent and in part pointedout hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevation of an oven of the present invention equippedwith heat sinks for receiving food-containing trays, auxiliary heatsources mounted above the heat sinks, and metallic covers for coveringthe trays (the trays being omitted from the view);

FIG. 2 is an enlarged sectional view of a portion of FIG. 1 but showinga tray positioned in a respective heat sink below its cover;

FIG. 3 is a perspective showing a heat sink, cover and auxiliary heatsource;

FIG. 4 is a plan of a cover per se;

FIG. 5 is a front perspective view of another embodiment of an oven ofthe present invention equipped with compartments for receivingfood-containing trays;

FIG. 6 is a sectional view of a portion of the oven of FIG. 5 showingtrays positioned in respective compartments below heat sources;

FIG. 7 is a sectional view of a portion of the oven similar to FIG. 6showing trays positioned in respective compartments below alternate heatsources;

FIG. 8 is a sectional view of a portion of the oven similar to FIG. 6showing trays positioned in respective compartments below alternate heatsources;

FIG. 9 is a sectional view of a portion of the oven of FIG. 5 showing aventilation system of the oven according to an embodiment of theinvention;

FIG. 10 is a perspective view of one embodiment of a tray used with theoven of FIG. 5;

FIG. 11 is a schematic diagram of one embodiment of a control circuit ofthe oven of FIG. 5;

FIG. 12 is a diagram of a time vs. temperature curve illustrating onemode of operation of the oven of FIG. 5;

FIG. 13 is a time vs. heat source activation curve for the mode ofoperation depicted in FIG. 12;

FIG. 14 is a diagram of a time vs. temperature curve illustrating adifferent mode of operation of the oven of FIG. 5;

FIG. 15 is a time vs. heat source activation curve for the mode ofoperation depicted in FIG. 14;

FIG. 16 is a perspective of a different embodiment of a holding oven ofthis invention;

FIG. 17 is a front elevation of the holding oven of FIG. 16;

FIG. 18 is a section on line 18-18 of FIG. 17;

FIG. 19 is an enlarged portion of FIG. 17 with parts broken away to showthe distance D1 between the food in the oven and a heat source of theoven;

FIG. 20 is a right-side elevation of the holding oven of FIG. 16;

FIG. 21 is a section on line 21-21 of FIG. 20;

FIG. 22A is a graph of a time v. holding temperature curve during anembodiment of a holding duration;

FIG. 22B is a graph of time v. radiant energy curve during theembodiment of FIG. 22A;

FIG. 23 is a schematic view of a holding oven of another embodiment;

FIG. 24 is a schematic view of a holding oven of still anotherembodiment; and

FIG. 25 is a schematic view of a holding oven of yet another embodiment.

Corresponding parts are designated by corresponding reference numbersthroughout the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates one embodiment of a holding oven of the presentinvention, generally designated 1, comprising a cabinet having aninterior 12 comprising a plurality of tiers for removably receiving aplurality of trays, each generally designated 3, the trays in each tierbeing disposed side-by-side. As shown, the oven has two tiers, an uppertier 5 and a lower tier 7, each accommodating three trays. It is to beunderstood that the number of tiers and the number of trays in each tiermay vary.

The holding oven 1 has a top 9, bottom 11, sides 13 and 15, and a shelf17 extending from one side to the other generally midway of the top andbottom. The shelf 17 and top 9 define the upper tier 5; the bottom 11and shelf 17 define the lower tier 7. The oven has a front panel 19 anda corresponding rear panel (not shown) each having openings such asindicated at 21 for sliding each tray 3 either into or out of itsrespective tier front or rear.

In one embodiment, each tray 3 is generally rectangular in plan, havinga bottom 23, opposite side walls each designated 25, and end walls eachdesignated 27. Each tray is disposed in its respective tier 5, 7 in theoven 1 in a heat sink generally designated 29 extending from front torear in the respective tier, being slidably disposed in its heat sinkfor being slidably withdrawn from or entered in the heat sink eitherfront or rear through the respective opening 21. Each heat sink 29,which is made of aluminum, for example, has a bottom 31 and side wallseach designated 33 (FIG. 2). The side walls 33 have outwardly(laterally) extending flanges 35 and rims 37 extending up from the outermargins of the flanges. Each heat sink constitutes a tray-receivingmember for holding a single tray. An electrical resistance heatingelement generally designated 39 having a bottom component 41 contactingthe bottom of the heat sink and upwardly extending side components 43contacting the sides of each heat sink is provided for heating the heatsink and the tray 3 therein. Each heat sink 29 and associated heatingelement 39 constitutes the primary heating source for heating therespective tray 3 and its food content. At 45 is indicated an on-offelectrical power control for all the heating elements 34. At 47, areindicated temperature controls for the heating elements 39 in the upperand lower tiers. The bottom component 41 of each heating element 39 inthe upper tier 5 seats on shelf 17, the bottom component 41 of eachheating element 39 in the lower tier 7 seats on the bottom 11 of theholding oven 1. The sides 43 of each heating element extend up to theflanges 35 of the respective heat sink 29. Reference may be made to U.S.Pat. Nos. 6,175,099, 6,262,394 and 6,541,739, incorporated herein byreference, assigned to Duke Manufacturing Co. of St. Louis, Mo., forfurther details relating to the construction of the heat sink 29 andassociated equipment.

Primary heating sources other than the heat sinks 29 and associatedheating elements 39 can be used without departing from the scope of thisinvention.

In the preferred embodiment, each tray 3 has a rim 49 having anoutwardly (laterally) directed upper part 51 with a downwardly extendingangled lip 53 in sliding sealing engagement with the respective heatsink flange 35. The rim defines the open top 32 of the tray 3. A covergenerally designated 55 is provided for the open top of each tray, eachcover having a metallic portion 57 overlying the top of the respectivetray. More specifically, the metallic portion 57 of each cover comprisesa generally horizontal cross wall comprising a rectangular plate ofanodized aluminum sheet, for example, having downturned flanges such asindicated at 59 at each side thereof and anodized metal angles 61extending the length thereof on each side margin. The lower edges of thedownturned flanges 59 engage the top of the heat sink flanges 35. One ormore of the covers 55 is/are spaced above the rims 49 of respectivetrays 3 at a distance no greater than one inch, more preferably nogreater than about 0.40 inch, and still more preferably no greater thanabout 0.30 in. One or more openings such as indicated at 63 is/areprovided in at least one of the covers 55 for venting moisture from eachtray having such an opening or openings. FIG. 4 shows a cover havingsixteen openings 63 arranged in a pattern such as illustrated. Thenumber and pattern may vary widely; the area of the one opening in acover having one opening and the combined area of the openings in acover having more than one opening is preferably less than about 25% ofthe area of the open top of the tray 3 it is covering, more preferablyless than about 5% and even more preferably less than 1% thereof. Thecombined areas of the openings and the specific pattern of openings in acover will vary depending on the type and quantity of food in the traybeing covered. Whatever the circumstances, the size and pattern of theopening(s) can be selected to closely control the amount of moisturevented from the tray and thus optimize the conditions for maintainingfood quality over an extended period of time.

Each cover 55 is part of a system generally designated 65 for heatingthe food in the respective tray in addition to the primary heat source,e.g., the respective heat sink 29 and heating element 39. This auxiliaryheating system 65 comprises a heat source 67 for heating the metallicportion 57 of the respective cover 55 whereby the metallic portion isadapted to emit radiant heat to the food in the respective tray foradditional warming of the food in the tray 3. Each heat source 67, whichis located over the respective cover 55, comprises one electric heatingelement 69 or more disposed in a sheet metal housing 71 affixed to aninterior surface of the oven or cabinet 1. In particular the heatingelement 69 is a commercial item, viz., a Chromalox electrical resistanceheater element sold by Carlton Company of St. Louis, Mo. The housing 71comprises a shallow pan of sheet metal such as aluminum having arectangular bottom 73, sides 75, ends such as indicated at 77 andflanges 79 extending out from the top of the sides.

In one embodiment, the heating element 69 lies on the bottom 73 of thepan extending lengthwise thereof. It is suitably connected in anelectrical circuit such that it is adapted to heat the respective cover55 by heating the bottom 73 of the pan 71 with attendant emission ofheat from the bottom of the pan to the cover. Terminals of the heatingelement for connection thereof in the aforesaid circuit are indicated at81 and 83. The pans 71 are affixed in the oven or cabinet with thebottom 73 of each pan 71 spaced above the respective cover 55 a distanceless than 2.0 inches and more particularly less than about 1.0 inch. Inone embodiment, the power delivered by each heat source 67 to therespective cover 55 ranges from 100-500 watts, for example, and eachheat source 67 is operable to heat each cover 55 to a temperature whichpreferably ranges from 200° to 500° F. Pivoted locks for locking thecovers 55 in the oven 1 are indicated at 85.

FIG. 5 illustrates a second embodiment of a holding oven of thisinvention, generally designated 101, comprising a generally rectangularor box-shaped cabinet 102. The cabinet 102 has a top 109, a bottom 111,opposite sides 113 and 115, a front panel 119 and a corresponding rearpanel (not shown). The cabinet 102 defines an interior, generallydesignated 112, for removably receiving a plurality of trays, eachgenerally designated 103. The holding oven 101 has vertical partitions126 and horizontal partitions 127 within the cabinet 102 dividing theinterior 112 thereof into a plurality of separate, thermally isolatedholding compartments 128. It is to be understood that the number ofvertical and horizontal partitions 126 and 127 (and thus the number ofcompartments 128) may vary. Preferably, the partitions 126 and 127prevent the transfer of food flavors between the compartments 128.

The front panel 119 and rear panel contain openings, such as indicatedat 121, in communication with each compartment 128. In one embodiment,the openings 121 in the front panel 119 have corresponding openings (notshown) formed in the rear panel such that each compartment 128 extendsfrom front to rear of the oven 101 and is adapted for removablyreceiving one of the trays 103 from either the front or the back of theholding oven 101. The openings 121 are sized for sliding each tray 103either into or out of the compartment 128.

Preferably, the compartments 128 and corresponding openings 121 arearranged in several tiers of compartments. As shown in FIG. 5, theholding oven has three horizontal tiers, an upper tier 132, a middletier 134 and a lower tier 136. Each tier includes three compartments128, with each compartment accommodating an individual tray 103. It isto be understood, however, that the number of tiers and the number ofcompartments in each tier may vary. In some embodiments, for example, itmay be desirable to configure the holding oven 101 to have a single tierhaving two, three, or more compartments 128. Preferably, the entirecabinet 102 is fabricated of sheet metal material and a least the top109, the bottom 111 and the sides 113 and 115 are of a dual wallconstruction to insulate the interior 112.

The holding oven 101 includes a control mechanism, generally indicatedat 140, for controlling operation of the oven 101. Preferably, thecontrol mechanism 140 has an operator input device, which in oneembodiment, comprises a keypad, indicated by reference 142, and adisplay, indicated by reference 144, to selectively allow the operatorto interact with the control mechanism to control the environment, suchas the temperature and/or air flow, in each compartment 128. The controlmechanism may include a separate keypad for each compartment 128.Alternately, the operator input device can include dials, switches andthe like known to those in the art. For example, rotatably mountedcontrol dials mounted on the front panel 119 and movable in apush-and-turn fashion to any user-selected positions can permit operatorinput to the control mechanism 140. The control mechanism 140 may alsoinclude associated indicator lights (not shown) to inform an operator ofthe status of a particular compartment 128 or the food within thecompartment, such as whether the temperature in the compartment is at adesired temperature or whether the food in the compartment isapproaching or has exceeded the desired hold time. Further operation ofthe control mechanism 140 will be described below.

Referring to FIGS. 6-8, each compartment 128 has tray supportscomprising, in one embodiment, inwardly (laterally) extending flanges144 extending from the vertical partitions 126 at opposite sides of thecompartment 128. The flanges 144 are vertically spaced for supporting atray 103 at different elevations in the compartment 128. In oneembodiment, the compartments 128 in the holding oven 101 have differentwidths and/or heights to accommodate trays of different sizes. It iscontemplated that the tray supports can have other forms, such asgrooves or slots in the vertical partitions 126.

Heat sources 146 positioned above respective compartments 128 areadapted to emit radiant heat into the compartments directed at the trays103 to warm food contained therein. Each heat source 146 can function asthe primary heating source for heating the respective tray 103 andcooking its food content or maintaining an already cooked food near aselected temperature. In the embodiment shown in FIG. 6, the heat source(designated 146A) is a quartz infrared heat source, but it will beunderstood that other heat sources may be used. For example, FIG. 7illustrates ceramic infrared heat sources 146B and FIG. 8 illustratesresistance heating elements embedded in magnesium oxide 146C.Alternatively, halogen infrared heat sources or other sources may beused. The power delivered by each heat source 146 ranges from betweenabout 20 and 2,000 watts, desirably between about 25 and 1500 watts,preferably between about 30 and 1000 watts, more preferably betweenabout 35 and 750 watts and even more preferably between about 40 and 600watts. In one embodiment, each heat source 146 delivers about 400 wattsof power. Additional means for heating the holding oven 101 other thanheat sources 146 can be used without departing from the scope of thisinvention. Reference may be made to the aforementioned U.S. Pat. Nos.6,175,099, 6,262,394 and 6,541,739, for further details relating to theconstruction of certain types of equipment used for heating the trays103 and food contained therein.

In one embodiment, a panel 150 is positioned between each heat source146 and its respective compartment 128 to prevent the trays 103 andtheir contents from contacting the heat sources. In one embodiment, thepanel 150 is a tempered glass cover that permits radiant energy producedby the heat source 146 to pass through into the compartment 128. In thisembodiment, the panel is preferably made from transparent orsemi-transparent glass. Alternately, the panel 150 can be a radiantmetallic plate. In this latter embodiment, the heat source 146 is usedto heat the panel 150, and the panel then radiates heat to warm thecontents of the tray 103. A reflector 152 is positioned above the heatsource 146 to radiate heat down toward the tray 103 below it.

FIG. 9 illustrates an embodiment of the holding oven 101 having a forcedair mechanism, indicated generally at 154, for delivering recirculatingair into the compartments 128. The mechanism 154 comprises lower airducting 160, upper air ducting 162, and a fan system 156 that moves airthrough the lower and upper air ducting air ducting. In one mode ofoperation, the fan system 156 circulates air in one direction along aflow path through the lower air ducting 160, into the compartments 128and then through the upper air ducting 162 and back to the fan system.The lower air ducting 160 conveys the forced air into the compartments128 through openings 164 located in a floor 166 of the compartments 128below the trays 103. Air flows up from the compartments 128 into theupper air ducting 162 through one or more openings 168 in the panels 150above the trays 103. In a second mode of operation, the fan system 156moves air in the opposite direction through the upper air ducting 162,down into the compartments via openings 168, into the lower ducting 160via openings 164, and then back to the fan system.

The number and pattern of openings 164, 168 in the panels 150 and floor166 may vary widely depending on the type of heat source 146 used ineach compartment 128 and the type of food in the compartment. The sizeand/or speed of the fan system 156 and/or the number, pattern and/orsize of the openings 164, 168 associated with each compartment 128 canbe varied to regulate the air flow around each tray 103 to provideoptimum air flow for different food products. Additionally, the number,size and/or pattern of the opening(s) 164, 168 can be selected toclosely control the amount of moisture vented from each compartment 128and thus optimize the conditions for maintaining food quality over anextended period of time.

An upper duct heat source 170 and a lower duct heat source 172 arepositioned in the respective air ducting 162,160 for heating air flowingalong the selected flow path. The upper and lower duct heat sources 170,172 heat the air that flows through the compartments so that,optionally, the food may also be warmed by convective heating. The ductheat sources 170, 172 are commercially available items, e.g., Chromaloxelectrical resistance heater element sold by Carlton Company of St.Louis, Mo. The duct heat sources 170, 172 may be used when additionalheat is needed in the compartments 128, such as when the initialtemperature is low or a large quantity of food is placed in thecompartments. In one embodiment, temperature sensors 174 (FIG. 9), suchas conventional resistive thermal detector type sensors known to thoseskilled in the art, may be positioned in each of the compartments 128 orin the air ducting 162, 160. The temperature sensors 174 providefeedback to the control mechanism 140, for example, to supply anindication of the temperature to the display 144, to control theoperation of the fan system 156, or to provide indications to a warningsystem (not shown) that the temperature has exceeded a selectedthreshold. The forced air mechanism 154 can also provide recirculatingair for forced cooling of the food stored in the compartment 128. FIG. 9illustrates a holding oven with a single tier and a single forced airmechanism 154, but holding ovens 101 with multiple tiers can haveseparate fan systems with associated air ducting 160, 162 for each tierwithin the scope of the invention.

The air flow over the food in the tray 103 is controlled to enable anoperator to control the amount of moisture that evaporates from thefood. When the air flow direction is from the bottom to the top, i.e.,from the lower air ducting 160 through the compartment 128 and into theupper air ducting 162, convection heat is applied to the food in thetray from below the tray, and infrared heat is applied from the heatsources 146 above the tray 103. By changing the direction of air flow sothat air flows from top to bottom, the food can be cooked or held with acombination of convection heat and infrared heat directed from above thetray 103. Depending on the food in the tray, air flow can be maintainedcontinuously from one direction, e.g., always from bottom to top,throughout the cook/hold cycle. Alternately, the direction of the airflow can be reversed during the cook/hold cycle so that air flow isalternately directed from the bottom and from the top of the foodproduct. In one embodiment, the forced air mechanism 154 supplies airwhile the heat sources 146 are activated and is turned off when the heatsources are deactivated.

Referring now to FIG. 10, each tray 103 is generally rectangular inplan, having a bottom 180, opposite side walls each designated 182, endwalls each designated 184, and an open top. As shown, each tray 103 hasa rim 186 comprising a pair of laterally extending lips 190 adapted forsliding sealing engagement with the respective support flanges 144 in acompartment. One or more openings such as indicated at 194 is/areprovided in at least one of the bottom 180 and/or the side walls 182 andend walls 184 for allowing air to circulate through the tray 103 to ventmoisture from each tray. FIG. 10 shows a tray having sixteen openings194 in the bottom 180 and each side wall 182 and 8 openings 194 in eachend wall 184 arranged in a pattern such as illustrated. It iscontemplated that the number, pattern and size of openings 194 may varywidely. For example, the openings 194 in the tray 103 may be circular,oval, square or other shape and each opening may have an area of betweenabout 0.1 and about 1.0 square inch. It is desirable that the combinedarea of the openings 194 in the tray is less than about 50% of the areaof the open top of the tray 103, preferably less than about 25% and morepreferably less than about 10% thereof. Also, it is contemplated thatdifferent trays 103 within the oven 101 may have different patterns ofopenings 194. The combined areas of the openings 194 and/or the specificpattern of openings in the tray 103 will vary depending on the type andquantity of food in the tray 103. Whatever the circumstances, the sizeand pattern of the opening(s) 194 can be selected to closely control theamount of moisture evaporated from the tray 103 and thus optimize theconditions for maintaining food quality over an extended period of time.

The control mechanism 140 is used to selectively control theenvironment, such as the temperature and/or air flow, in eachcompartment 128 of the holding oven 101. As will be described more fullyhereafter, the control mechanism 140 is operable to vary the amount ofradiant heat as needed to maintain the food at a desired holdingtemperature to preserve the quality of the food for a longer period oftime. As used herein, the term “selected holding temperature” meanseither a single substantially constant temperature (e.g., 180° F.) or arange of temperatures (e.g., 160-180° F.). In one embodiment, thecontrol mechanism comprises suitable timer and duty cycle controls tocontrol the length of the duty cycle of each heat source 146, the term“duty cycle” meaning the ratio of heat source on-time to heat sourceon-time plus heat source off-time. The control mechanism 140 uses asuitable microprocessor and appropriate software to control relays 198(FIG. 11) that activate the heat sources 146, 170 and 172 and fans 156.

FIG. 11 is a simplified schematic of a portion of one embodiment of anoven control circuit, generally indicated at 196, that is controlled bythe control mechanism 140. The circuit 196 operates the heat sources 146in the multiple compartments 128 of the holding oven and the heatsources 170, 172 in the upper and lower ducting 160, 162. In theembodiment shown, the control mechanism 140 regulates the heat sourcesin the holding oven 101 by energizing conventional relays 198. It isunderstood that the control mechanism 140 may independently operate theheat sources 146 in the compartments 128, such that the heat source 146for one compartment may be actuated while the corresponding heat sourcefor another compartment is at a different level of activation ordeactivated. Additionally, the control mechanism 140 may independentlyoperate the upper and lower duct heat sources 170, 172 such thatneither, one or both heat sources in a flow path may be operating, andsuch that, for example, the top heat source may be operated in one tierwhile the bottom heat source may be operated in another tier. Using akeypad 142 or other suitable operator input device, the controlmechanism 140 can be programmed to control the heat sources 146, 170 and172 to adjust various parameters, such as, for example, the ambient holdtime, the heated hold time, the total hold time, the percentage heateron time, the time base of the duty cycle, the cook or rethermalizationtime, and/or the temperature, as more fully described below. As such,the control mechanism 140 controls operation of the heat sources 146independent of one another so that the temperature in each compartment128 may be independently controlled.

Typically, the holding oven 101 will operate in at least two modes. In afirst “cool down and hold” mode, the initial temperature of the foodplaced in the holding oven is higher than the desired holdingtemperature of the food, as is typically the case when the food has justbeen cooked in a cooking appliance (e.g., cooking or baking oven, frier,etc.) and then is transferred to the holding oven. In this mode, thecontrol mechanism 140 is operable to maintain the heat source in arespective compartment 128 deactivated (or at a low level of activation)while the pre-cooked food in the compartment 128 cools down to theselected holding temperature during a duration of non-heated holdingtime, and for then controlling the heat source 146 in the compartment128 to maintain the food in the compartment 128 at or near the selectedholding temperature for a duration of heated holding time. In a second“heat up and hold” or “rethermalizing” mode, the initial temperature ofthe pre-cooked food placed in the oven is lower than the desired holdingtemperature of the food, as where the food has been cooked and thenrefrigerated before placement in the holding oven. In this mode, thecontrol mechanism 140 is operable to activate the heat source in thecompartment 128 to raise the temperature in the compartment 128 to theselected holding temperature during a duration of rethermalizing holdingtime, and for then controlling the heat source 146 in the at least onecompartment 128 to maintain the food in the compartment 128 at theselected holding temperature for the duration of heated holding time. Itwill be understood that the oven 1 of FIG. 1 can be used in a similarmanner without departing from the scope of the invention.

FIGS. 12 and 13 illustrate an example of the operation of the holdingoven 101 in the first (cool down and hold) mode. In particular, FIG. 12illustrates a time vs. temperature curve for a complete duration ofholding time D for one compartment 128 of the oven 101, and FIG. 13illustrates a time vs. activation curve for the heat source 146 of thatsame compartment during the holding time duration D. The time vs.temperature curve of FIG. 12 plots the temperature of the food productas a function of time. One skilled in the art will understand that thiscurve can be different for each type of food product to be held in theoven 101.

In a cool down and hold situation, a food product is typically cooked asby frying, grilling, baking, etc., in a cooking appliance until adesired high internal temperature, usually between about 170 and 210degrees Fahrenheit (° F.), is achieved. After the food is cooked, thefood product is placed in a tray 103 and inserted into compartment 128in the oven 101. Alternatively, the food can be placed in the ovenwithout the use of a tray. Using the keypad 142 or other input device,the operator selects a desired holding temperature, indicated at T,which will be lower than the temperature Tc of the food initially placedin the compartment. The holding temperature T is the desired temperaturefor maintaining the pre-cooked food to preserve taste, appearance and/orother food quality. The operator also selects a duration of holding timeD. The duration of holding time D is the total time the food is to beheld in the oven 101 and maintained at a desired quality level.Alternatively, the control mechanism 140 can be programmed so that theoperator need only select the type of food to be placed in thecompartment and the control mechanism 140 automatically uses preselectedsettings for that type of food.

In general, when the holding oven is operating in the cool down and holdmode, it is desirable that food introduced into the oven be allowed toquickly cool down to the selected holding temperature, and that the foodbe held at this temperature thereafter. Thus, the duration of holdingtime D may comprise an ambient hold time, i.e., a period of non-heatedcool-down time such as indicated at B in FIG. 12, during which time thefood product is allowed to cool to the desired holding temperature T.Preferably, during the ambient hold time B, heat source 146 is either ina deactivated state or a state in which it is delivering a relativelylow quantity of radiant heat to the food so that the food product maycool down more rapidly than if the heat source was at full power. Thefood product is allowed to cool for the ambient hold time B until itreaches the desired hold temperature T as illustrated at point A. In oneembodiment, forced air flow from the forced air mechanism 154 (FIG. 9)can be used to more rapidly decrease the temperature. After the internaltemperature of the food decreases to the desired hold temperature T, thefood is held near the desired hold temperature to preserve food qualityfor a period of heated hold time, indicated at C, comprising theremaining portion of the holding time duration D. During the heatedholding time C, the heat source 146 may be operated in duty cycles toapply the appropriate amount of radiant heat to the food. Additionally,the control mechanism 140 controls the heat sources 170, 172 and the fansystem 156 to maintain the internal food temperature at or near thedesired hold temperature T during the heated hold time C.

FIG. 13 illustrates an embodiment in which the heat source 146 issuccessively activated and deactivated in a controlled sequence or dutycycle, indicated at G, to maintain the temperature in the compartment128 near the selected holding temperature T. In this particularembodiment, each duty cycle G comprises a heating interval E duringwhich time the heat source 146 is activated followed by a non-heatinginterval F during which time the heat source is deactivated. Thetime-base of the duty cycle G is the time required to complete one cycleof activation and deactivation of the heat source 146 as shown in FIG.13. In one embodiment, the time-base of the duty cycle G and the percenton time of the heat source 146 (i.e., the duration of heating interval Edivided by the time-base of the duty cycle G expressed as a percent)maintains the actual temperature within the compartment 128 within atleast about 15 degrees of the desired temperature, preferably within atleast about 10 degrees, more preferably within about 5 degrees, and evenmore preferably within about 2 degrees of the desired temperature.

The operator is able to set various parameters using the keypad 142 orother input device of the control mechanism 140, such as the ambienthold time delay B, the heating interval E, the time-base of the dutycycle G, and/or total hold time D. These parameters can be selected bythe operator or preset for the type of food product in the compartment128 so that the operator need only select the proper food product. Thecontrol mechanism 140 in an oven 101 having more than one compartment128 can control the duty cycle of the heat source 146 in eachcompartment to maintain the temperatures in the compartments atdifferent levels.

Using the keypad 142 or other input device, an operator can also controlthe operation of the forced air mechanism 154 (FIG. 9) by activating thefan system 156 or selecting the direction of forced air flow. In oneembodiment, forced air flow from the forced air mechanism 154 conveysconvective heating air into the compartments 128 at locations below thetrays 103 for flow in a generally upward direction toward the trays 103.Alternately, the ventilation system conveys heating air into thecompartments 128 at locations above the trays 103 for flow in agenerally downward direction toward the trays 103. The fan system 156can be operated such that heating air is circulated through thecompartments 128 in one direction and then the direction of air flow isreversed to circulate heating air through the compartments 128 in theopposite direction. Using the keypad 142 or other input device of thecontrol mechanism 140, the operator is able to select the duration thatthe fan system 156 circulates air through the compartments 128. Forexample, in one embodiment, the forced air mechanism 154 operates in acontrolled sequence during the duty cycle G such that the fan system 156is activated when the heat sources 146 are activated and is deactivatedwhen the heat sources are deactivated. Alternately, the fan system 156can be continuously activated for the duration of the total hold time Dor can be activated so that the fan system is on a desired percentage ofthe duty cycle G independent of the heat sources. Preferably, the fansystem 156 is activated a suitable percentage of the time to control theevaporation of moisture from the food in the compartment 128. Thepercentage of time the fan system 156 is activated desirably depends onthe type and/or the amount of food placed in the compartment 128. Thepercentage of time the fan system 156 is activated and the direction ofair flow can be selected by the operator or preset for the type of foodproduct in the compartment 128 so that the operator need only select theproper food product. Additionally, the vertical position of at least onetray 103 in a respective compartment 128 may be varied.

Set forth below are exemplary oven settings for particular food productswhen the oven is operating in a cool down and hold mode.

EXAMPLE 1 Fried Chicken Nuggets

-   -   Ambient hold time delay (B)=10 minutes    -   Hold temperature (T)=180° F.    -   Time-base of duty cycle (G)=120 seconds    -   Percent on time (E)=50%    -   Total hold time (D)=60 minutes

EXAMPLE 2 Fried Apple Turnover

-   -   Ambient hold time delay (B)=25 minutes    -   Hold temperature (T)=200° F.    -   Time base of duty cycle (G)=120 seconds    -   Percent on time (E)=40%    -   Total hold time (D)=240 minutes

FIGS. 14 and 15 illustrate an example of the operation of the oven 101in the second (heat up and hold or rethermalizing) mode. In particular,FIG. 14 illustrates a time vs. temperature curve for a complete holdcycle D for one compartment 128 of the oven 101, and FIG. 15 illustratesa time vs. activation curve for the heat source 146 of that samecompartment during the hold cycle D. The time vs. temperature curve ofFIG. 14 plots the temperature of the food product as a function of time.One skilled in the art will understand that this curve can be differentfor each type of food product to be held in the oven 101.

In this mode, the oven 101 is used to raise the temperature of a foodproduct to a selected temperature and hold the food product at theselected temperature. A tray 103 containing a food product at an initialtemperature T₁ is placed into the compartment 128. (Temperature T₁ mayvary from a frozen or refrigerated temperature to ambient or above.)Using the keypad 142 or other input device, the operator selects adesired holding temperature T (which will be higher than the initialfood temperature T_(I)), and a duration of holding time D.Alternatively, the control mechanism 140 can be programmed so that theoperator need only select the type of food to be placed in thecompartment and the control mechanism 140 automatically uses preselectedsettings for that type of food. In either case, the control mechanism isoperable to activate the heat source 146 to raise the temperature of thefood product for a duration of heat-up or rethermalization time,indicated at I, the food reaching the holding temperature T at time H.The heat source 146 is then activated and deactivated during the heatedholding time C for successive duty cycles G to maintain the food in thecompartment 128 at the selected holding temperature T for the durationthe total hold time D. In one embodiment, the duration of the heatedholding time C includes intervals of the duty cycle G when the heatsource 146 is activated as indicated by E and intervals during which theheat source is deactivated as indicated by F as described above.

Set forth below are exemplary oven settings for particular food productswhen the oven is operating in a heat-up and hold mode.

EXAMPLE 3 Diced Frozen Chicken

-   -   Rethermalization time (I)=40 minutes    -   Hold temperature(T)=220° F.    -   Time-base of duty cycle (G)=180 seconds    -   Percent on time (E)=50%    -   Total hold time(D)=160 minutes

EXAMPLE 4 Refrigerated Beef BBO

-   -   Rethermalization time (I)=30 minutes    -   Hold temperature(T)=210° F.    -   Time base of duty cycle (G)=180 seconds    -   Percent on time (E)=30%    -   Total hold time(D)=240 minutes

With the heating system of the present invention and the capability ofcontrolling the evaporation of moisture from the trays 103, the holdingtime (D) for fast service cooked foods such as chicken and french friesis substantially increased, and good texture and taste are maintained.In this respect, controlling the rate of evaporation of moisture fromchicken, for example, precludes drying out and toughening of the chickenfibers and precludes the breading from becoming dry and greasy. And withrespect to french fries, for example, development of a dry, rubberytexture as moisture is lost and the outer skin loses crispness isprecluded.

In the embodiments described above, the control mechanism 140 uses aduty-cycle system to control the amount of radiant heat delivered to thepre-cooked food by the heat sources. In this type of system, thepercentage of heater on and off time is adjusted to vary the radiantenergy as needed to maintain the food at the suitable holdingtemperature. It will be understood, however, that the control mechanism140 can vary the amount of radiant energy delivered to the food in otherways. For example, the heat sources 146 may be variable-power heatersoperable to deliver radiant heat at multiple discrete energy levels orat an infinite number of levels between full-power and zero power (as byvarying the voltage to the heaters), and the control mechanism 140 mayoperate to increase and decrease the radiant heat delivered by theheaters in a controlled, pre-programmed manner to maintain a particularfood at its ideal holding temperature.

The particular program used by the control mechanism 140 to control aheat source 146 for any given type of food may be determinedempirically. Alternatively, the control mechanism 140 can include one ormore sensors and one or more appropriate feedback loops for eachcompartment or group of components of the holding oven. For example, inone embodiment, at least one sensor is used in each compartment todetect a characteristic indicative of the temperature of the food in thecompartment, and the control mechanism is responsive to signals receivedfrom the at least one sensor to control the heat source 146 to vary theradiant heat delivered to the pre-cooked food to maintain it at aholding temperature appropriate for that food. The characteristicdetected by the one or more sensors may be the temperature of the air inthe compartment, or the temperature of a surface in the compartment, orthe radiant IR energy emitted by the food in the compartment, or someother characteristic. Thus, the sensor may be a standard temperaturesensor, or an IR emissions detector, or some other type of detectorcapable of detecting the aforesaid characteristic indicative of thetemperature of the food in the compartment.

FIGS. 16-21 show another embodiment of food warming apparatus of thisinvention, generally designated 201. The apparatus comprises a cabinet203 having two horizontal tiers of compartments, two compartments pertier (each compartment being designated 207). It will be understood thatthe number of tiers can vary from one to any number more than one, andthat the number of compartments 207 in each tier may vary from one toany number more than one. In the particular embodiment shown, eachcompartment is sized to receive a single tray T, but it will beunderstood that each compartment 207 may be sized to receive more thanone tray, or that some compartments may be sized to receive one tray andother compartments more than one tray. In other embodiments (to bediscussed later), food is placed in one or more compartments 207 withoutthe use of a tray.

The cabinet 203 has front and back panels 211, 213 with openings 215aligned with the compartments 207 in the cabinet to allow food (eitherin or out of trays T) to be placed into the compartments and removedfrom the compartments from both ends of the compartments. The cabinetalso has a bottom wall 221, side walls 223, a top wall 225, a verticalpartition or divider 227 extending between the top and bottom walls ofthe cabinet to separate the two compartments 207 in each tier, and ahorizontal partition or divider 231 extending between the side walls 223to separate the compartments in the upper tier from the compartments inthe lower tier. As a result, the interior of the cabinet is divided intoa plurality of separate, thermally isolated holding compartments 207,and each compartment is completely enclosed on opposite sides, top andbottom so that food flavors are prevented (or at least inhibited) fromtransferring between compartments. Suitable thermal insulation (notshown) is provided adjacent the walls of each compartment 207.

As shown in FIG. 19, for example each compartment 207 has a heat source235 for emitting radiant heat down on pre-cooked food in thecompartment. As noted previously, this heat source 225 may comprise oneor more IR heat lamps or the like, each mounted by a suitable fixtureadjacent to the top wall of the compartment. A reflector 241 is providedin each compartment 207 over the best source 235 for reflecting radiantheat in a generally downward direction through a cover panel 245 ofsuitable material capable of transmitting the heat (e.g., glass). Thefood in the compartment 207 is positioned a distance D1 below the heatsource 235, as shown in FIG. 19. Distance D1 is desirably relativelysmall to reduce or minimize the size (e.g., vertical height) of thecabinet 203. In one embodiment, for example, distance D1 is less than 12in.; in another it is less than 11 in.; in another it is less than 10in.; in another it is less than 9 in.; in another it is less than 8 in.;in another it is less than 7 in.; in another it is less than 6 in.; inanother it is less than 5 in.; in another it is less than 4 in.; inanother it is less than 3 in.; in another it is less than 2 in.; inanother it is less than 1 in.; and in another it less than 0.5 in. Inother embodiments, distance D1 may be in the range of 0.25 in. to 10in., or in the range of 0.25 in. to 8 in., or in the range of 0.25 in.to 6 in., or in the range of 0.25 to 4 in., or in the range of 0.25 to 3in., or in the range of 0.25 in. to 2 in., or in the range of 0.25 in.to 1 in. Where the pre-cooked food is placed in one or more trays, asshown in FIG. 19, each tray T is supported by supports 247 in arespective compartment 207 at an elevation where the bottom of the trayis spaced above the floor of the compartment a suitable distance D2.Distance D2 may be in the range of 0-12 in., and more preferably 0.5-1.0in. Alternatively, the food may be placed on the floor of thecompartment.

The heat sources 235 in the cabinet 203 are controlled by a suitablecontrol mechanism 251, similar to the control mechanism 140 describedabove, which can be used to operate each heat source 235 independentlyof the other heat sources to deliver varying amounts of radiant energyto the food in a respective compartment. In this manner, the amount ofradiant energy delivered to the food in a compartment 207 can be closelycontrolled to maintain the food at an appropriate holding temperaturefor that particular food, as described above. Also, because the amountof radiant heat delivered to the food is varied as a function of time,the heat source 235 in each compartment 207 can be placed much closer tothe food (e.g., distance D1 in FIG. 19, discussed above) which has thedesirable advantage of reducing the size of the cabinet 203. This is incontrast to conventional IR holding units where the energy delivered bythe heat source is not variable. Rather, the heat source is energized todeliver full power all of the time. As a result, the heat source must bepositioned relatively far from the food (e.g., 12 in. or more).

In one embodiment, the control mechanism 251 is programmed for differenttypes of food, so that after food has been placed in a particularcompartment 207, an operator simply selects that type of food from asuitable menu on a display (not shown) on the cabinet. The controlmechanism then automatically selects the appropriate heating protocolfor the food selected, including one or more of the following: the idealholding temperature for the food selected; the duration of holding time(“holding duration”); and the manner in which the heat source in eachcompartment is to be varied to maintain the food at the desired holdingtemperature (e.g., percent on time during each duty cycle, if dutycycles are used). For convenience, the control 251 also includes a timerwhich times out the holding duration, and a display 255 which shows thetime remaining until the end of holding duration. The control mechanism251 may also include a visual and/or audible alarm for alerting anoperator at a predetermined time before the end of the holding duration,so that steps can be taken to start cooking a fresh batch or batches ofadditional food. (At the end of a holding duration, any food remainingin the compartments 207 is typically disposed of and replaced by freshlycooked food.)

As noted previously, an important aspect of this invention is theability of the control mechanism 251 to vary the amount of radiant heatdelivered by the heat source in each compartment 207 to the pre-cookedfood in the compartment. In general, or at least typically, it isdesirable that pre-cooked food introduced into the compartment beallowed to cool down as quickly as possible to the desired holdingtemperature, and that the food be held relatively constant at thedesired holding temperature using a minimum of power to the heat source235. The graphs in FIGS. 22A and 22B illustrate this concept. FIG. 22Agraphs time v. temperature in one compartment 207. Pre-cooked foodintroduced into the compartment at time T₀ cools down to the desiredholding temperature at time T₁. Thereafter, the food is substantiallymaintained at the holding temperature for the remainder of the holdingduration D. FIG. 22B is a graph of time v. the radiant energy deliveredby the heat source 235 to the food. In the particular embodiment shownin this graph, the heat source is operated at a first relatively lowlevel (where the heater is either off or delivering radiant heat at lowlevel of energy or power) during a first phase P1 from time T₀ to timeT₁, so that little or no radiant energy is delivered to the food. As aresult, the temperature of the food declines relatively rapidly towardambient temperature. When the temperature of the food approaches (orreaches) the desired holding temperature, the control mechanism 251causes the heat source 235 in the compartment 207 to deliver radiantheat at a second higher level (e.g., 70% of maximum) to stop the declinein temperature of the food and hold it at about the desired holdingtemperature during a second phase P2 from time T₁ to time T₂. After thetemperature of the food has equilibrated at the desired holdingtemperature, which will vary depending on the particular type of food,the control mechanism 251 causes the heat source 235 to reduce theamount of radiant heat delivered to the food to a third level (e.g., 30%maximum) sufficient to maintain the food at the desired holdingtemperature during a third phase P3 from time T2 until the end of theholding period at time T3.

It will be understood that the graphs shown in FIGS. 22A and 22B canvary, and that the number of phases P1, P2, P3 discussed above can varywithout departing from the scope of this invention.

FIG. 23 shows another embodiment of a holding oven of this invention,generally designated 301. The oven is similar to those described aboveexcept that the cabinet of the unit has only one compartment. In thisembodiment, food is not placed in a tray, but rather on the bottom wall307 or other supporting surface in the compartment, and the heat source311 is closely spaced above the food to heat the food and maintain it atthe desired holding temperature. The spacing D1 between the food and theIR heat source is relatively small (as discussed above) to reduce theoverall height dimension of the oven 301. The heat source 311 iscontrolled by a control mechanism 140, 251 of the type described above.

FIG. 24 shows a holding oven, generally designated 401, which is similarto the oven shown in FIG. 23. In this embodiment, the single compartment403 of the oven is sized to hold multiple trays T. All other aspects ofthe oven, including the heat source and control mechanism, are the same.

FIG. 25 shows a holding oven, generally designated 501, which is similarto the oven shown in FIG. 24 except that the oven is divided into threecompartments 503, each of which is capable of receiving food placed onthe bottom wall or other supporting surface in the compartment.Partitions 507 between the compartments prevent or at least inhibit thetransfer of food flavors between adjacent compartments. Each compartment503 has its own heat source 511 which is spaced relatively closely tothe bottom wall of the compartment to maintain the distance between thefood and the heat source within the ranges (e.g., distance D1) describedabove. The heat sources 511 are controlled by a control mechanismsimilar to the control mechanism 140, 251 described above.

When introducing elements of the present invention or the preferredembodiment(s) thereof, the articles “a”, “an”, “the” and “said” areintended to mean that there are one or more of the elements. The terms“comprising”, “including” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained. Asvarious changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

1. A method of preserving cooked food, comprising the steps of: cookingfood in a cooking appliance to provide pre-cooked food; placing thepre-cooked food in a holding compartment of a food warming apparatus fora duration of holding time; and heating the pre-cooked food in theholding compartment for at least a portion of said duration of holdingtime by delivering in a pre-programmed manner an amount of radiant heatto the pre-cooked food from a radiant heat source positioned above thepre-cooked food; said heating step comprising varying the amount ofradiant heat delivered to the pre-cooked food to maintain the food at aselected holding temperature by delivering radiant heat to thepre-cooked food at a first level during a first phase of the duration ofholding time and delivering radiant heat to the pre-cooked food at asecond level during a second phase of the duration of holding time.
 2. Amethod as set forth in claim 1 wherein said first level and said secondlevel are both less than a maximum level of radiant heat deliverablefrom the radiant heat source.
 3. A method as set forth in claim 1wherein said first level of radiant heat permits said pre-cooked food tocool down to the selected holding temperature and said second level ofradiant heat is higher than the first level to hold the pre-cooked foodat the selected holding temperature.
 4. A method as set forth in claim 3wherein said heating step further comprises delivering radiant heat tothe pre-cooked food at a third level less than said second level duringa third phase of the duration to maintain said pre-cooked food at theselected holding temperature.
 5. A method as set forth in claim 1wherein said pre-cooked food placed in the compartment is at atemperature greater than ambient temperature, and said heating stepcomprises not delivering any substantial radiant heat to the pre-cookedfood until the food has cooled to a temperature approaching saidselected holding temperature.
 6. A method as set forth in claim 1wherein said pre-cooked food placed in the compartment is at atemperature below ambient temperature, and said heating step comprisesdelivering radiant heat to the pre-cooked food until the food reachessaid selected holding temperature.
 7. A method as set forth in claim 1further comprising sensing a characteristic indicative of thetemperature of the pre-cooked food in the compartment, and varying theamount of radiant heat delivered to the food according to said sensedcharacteristic.
 8. A method as set forth in claim 7 wherein said sensedcharacteristic is a temperature of a surface in said holdingcompartment.
 9. A method as set forth in claim 7 wherein said sensedcharacteristic is an amount of radiant energy emitted by said pre-cookedfood.
 10. A method as set forth in claim 1 further comprising placingsaid pre-cooked food in said holding oven at a location within adistance of less then 12 in. from said source of radiant heat.
 11. Amethod as set forth in claim 1 further comprising placing saidpre-cooked food in said holding oven at a location within a distance ofless then 10 in. from said source of radiant heat.
 12. A method as setforth in claim 1 further comprising placing said pre-cooked food in saidholding oven at a location within a distance of less then 8 in. fromsaid source of radiant heat.
 13. A method as set forth in claim 1further comprising placing said pre-cooked food in said holding oven ata location within a distance of less then 6 in. from said source ofradiant heat.
 14. A method as set forth in claim 1 further comprisingplacing said pre-cooked food in said holding oven at a location within adistance of less then 4 in. from said source of radiant heat.
 15. Amethod as set forth in claim 1 further comprising placing saidpre-cooked food in said holding oven at a location within a distance ofless then 2 in. from said source radiant heat.
 16. A method ofcontrolling a food holding oven, said oven comprising a cabinet, aplurality of separate, thermally isolated holding compartments in thecabinet, a plurality of trays for containing pre-cooked food having beenpreviously 5 cooked in a cooking appliance, each compartment beingadapted for removably receiving one tray per compartment, and heatsources above respective trays adapted for activation to emit radiantheat to the food in the trays to warm the food, said method comprising:setting a selected holding temperature for each compartment; setting aduration of holding time for each compartment, said duration of holdingtime comprising a duration of heated holding time; and varying theamount of radiant heat delivered to the pre-cooked food during arespective duration of heated holding time to maintain the food in arespective compartment at said selected holding temperature.
 17. Amethod as set forth in claim 16 wherein said varying the amount ofradiant heat comprises delivering radiant heat to the pre-cooked food ata first level during a first phase of the duration of holing time anddelivering radiant heat to the pre-cooked food at a second level duringa second phase of the duration of holding time.
 18. A method as setforth in claim 17 wherein said first level of radiant heat permits saidpre-cooked food to cool down to the selected holding temperature duringsaid first phase and said second level of radiant heat is higher thanthe first level to hold the pre-cooked food at the selected holdingtemperature.
 19. A method as set forth in claim 18 wherein said varyingthe amount of radiant heat further comprises delivering radiant heat tothe pre-cooked food at a third level less than said second level duringa third phase of the duration to maintain said pre-cooked food at theselected holding temperature.
 20. A method as set forth in claim 16further comprising maintaining at least two compartments at differentselected holding temperatures.
 21. A method as set forth in claim 16further comprising placing said pre-cooked food in a respectivecompartment at a location within a distance of less then 12 in. from arespective heat source.